Knots - partial suspension

[BabyCamus]

Please help I'm awful at knots - I tried to make a slipknot and I think I got it right but it ended up so that putting pressure downwards on the noose just made the noose bigger and then come undone. How do I make it so that the knot TIGHTENS as pressure is put on the noose (as you push your head down)?

Here is two pictures of my chosen ligature - lying on the floor stretched out (picture 1) and picture 2 shows the ligature hanging over the support that I will hang from - the shower door frame.


People who have more knot skills than me, please help!
Are there any videos for how to tie knots for partial suspension hanging?

 

[HerculePoirot]

Perhaps relevant, perhaps not: are you sure the shower upper bar will hold twice your weight? It's a minimum requirement, as you are likely to shake a lot...
See this:
Of course you'll need a bigger scarf. The video above is not intended for suicide, obviously.